Image intensification for sensitized films

ABSTRACT

In a process in which a spectral sensitizer is incorporated in a photosensitive composition to increase its sensitivity to light levels lower than ordinarily useful for inducing a light intensifiable latent image, the improvement wherein the sensitizer has a conjugated system including at least one ring and as a substituent on the ring a group which influences the electron density of the sensitizer to enhance the intensification propensity of the composition.

United States Patent Inventors Peter Bruck Encino; Nancy Gershman Adin, San Gabriel, both of Calif. Appl. No. 631,141 Filed Apr. 17, 1967 Patented Oct. 26, 1971 Assignee Bell & Howell Company Chicago, Ill.

IMPROVED IMAGE INTENSIFICATION FOR SENSITIZED FILMS 6 Claims, No Drawings U.S. Cl 96/27, 96/48, 96/90,96/89,96/119, 96/106 lnt.Cl G03c 5/04, G030 5/24 Field of Search 96/89, 90, 106,101, 48, 27

[56] References Cited UNITED STATES PATENTS 3,486,898 12/1969 Wainer 96/90 3,510,300 5/1970 Fatland et a1. 96/48 3,042,517 7/1962 Wainer 96/90 X 3,095,303 6/1963 Sprague et al. 96/36.3 3,099,558 7/1963 Levinos 96/36.3 3,189,456 6/1965 Hunt 96/106 Primary Examiner-Norman G. Torchin Assistant Examiner-Richard E. F ichter Attorney-Robert Berliner IMPROVED IMAGE INTENSIFICATION FOR SENSITIZED FILMS BACKGROUND OF THE INVENTION I ous treatment or by means of supplemental exposure, or by an assortment of various exposure combinations involving solarization and/or Herschel efiects. In the field of organic photochemistry, not involving the use of a silver halide salt to obtain an image, fewer intensification effects have been noted, but even here certain intensifiable systems have been demonstrated. For example, in U.S. Pat. No. 3,095,303 a photosensitive system is described comprising a styryl dye base, (4-(pdimethylaminostyryl)-guinoline), in combination with an organic halogen compound, wherein image-wise exposure causes conversion of the dye base to the quaternary salt, a colored dye, to yield a negative-working image. In that system,

' without intensification, high levels of exposure are required to obtain an image. However, by means of light intensification, e.g., with red light, moderate levels of imaging light can be used. Such procedures involve color-forming materials, in this case the styryl dye bases, which are themselves intensifiable. Other systems have been described using leuco crystal violet as the color-forming autointensifiable material; e.g., in U.S. Pat. No. 3,121,633 brief exposures to heat (or infrared) intensifies an exposed combination of leuco dye base and tribromoacetophenone.

In such systems, the intensifying radiation either has no color-forming effect on those areas of the film which were not previously exposed or else has a lesser effect than on such preexposed areas so that the intensification is sufficiently nonfogging to allow theproduction of a discernible image. Thus, it is known to intensify images obtained in photosensitive material where the photosensitive material itself yields an image that can be intensified. However, there are many photosensitive systems in which the exposed color-forming material does not alone intensify sufiiciently to form a useful image, e.g., many silver halide formulations, and many organic systems.

With organic systems, generally two or more organic materials are involved, other than merely dye bases, which react under the influence of actinic light to produce a color. As early as 1921, Murray C. Beebe and his coworkers described numerous organic photographic systems (e.g., U.S. Pat. Nos. 1,574,357; 1,574,358; 1,574,359; 1,575,143; 1,583,519; 1,587,269; 1,587,519; 1,587,270; 1,587,271; 1,587,272; 1,587,273; 1,587,274; 1,604,674; 1,618,505; 1,655,127; 1,658,510; and 1,820,593). Generally, these systems relate to the use of organic halogen compounds (e.g., iodoform and others) in combination with a second material, in which Beebe and subsequent workers have theorized that light effects the release of a radical from the halogen compound which carries out a color-framing reaction with the second material. Subsequent workers such as Eugene Wainer (e.g., U.S. Pat. Nos. 3,042,515; 3,042516; 3,043,517; 3,042,518; 3,042,519; 3,046,125; and 3,056,673 and Robert Sprague U.S. Pat. No. 3,082,086), as well as a number of other workers since the time of Beebe, have continued the development of various photographic systems involving photo-energized reactions of combinations of halogen-containing compounds and one or more other compound. Other recent disclosures include British Pat. No. 917,919 and Belgian Pat. No. 596,094. It has also been discovered that incorporation of the above combinations as dispersions in a continuous phase, e.g., gelatin, in which such combinations are substantially insoluble, results in photographic compositions of superior speed, sensitivity and other properties, including, with certain reactants, the ready ability to yield positive-mode pictures, e.g., as described in Belgian Pat. 647,584 and in the above noted applications of Y. Yamada and T. H. Garland.

More recently, it has been found that photosystems as described above and others can be photolatensified by incorporating a material that imparts a photo-latensification propensity to the photosystem. Thus, a sensitizer is incorporated that upon imagewise exposure confers on the composition, in areas of such exposure, increased sensitivity to radiation in a spectral region of lower sensitivity in absence of the sensitizer. The imaged composition is then subjected to such lower sensitivity radiation and the latent image formed upon first exposure is thereby intensified. For example, the photosystem comprising N-vinylcarbazole and carbon tetrabromide, dispersed in gelatin, can yield a positive image under average daylight conditions, and appropriate post-exposure treatment, with an exposure of several seconds.-By adding a sensitizer, such as 4-(p-dimethylaminostyryl) quinoline, exposure time can be reduced to one or two seconds to obtain a good positive image. However, if after exposure the composition is blanket exposed to suitable latensifying radiation, in this case red light, good positive images can be. obtained with initial exposures of only fractions of a second.

The foregoing and other latensification procedures are described in detail in the above referenced application by Y. Yamada and T. H. Garland entitled PHOTOGRAPHIC PROCESS." The application notes that the sensitizer imparts sensitivity, upon image-wise exposure, to radiation in a region to which the original material has relatively lower sensitivity, so that upon blanket exposure to such radiation essentially only the imaged areas will be thereby affected. The application further notes that certain sensitizers may impart sensitivity only to radiation in a region to which the original material is highly sensitive, and thus, with such sensitizers latensification is somewhat masked by fogging. In some other cases the imparted sensitivity, although into a relatively nonfogging region, is not of sufficient intensity to effect an entirely satisfactory latensification. Thus some sensitizers are relatively less effective than others.

SUMMARY OF THE INVENTION It electron now been found that the foregoing, relatively less effective, sensitizers can be improved in their ability to latensify by providing the sensitizer with a molecular group that influences its electron density. In accordance with one aspect of our invention, we provide a means for improving the latensification propensity of a sensitizer by providing it with a substituent that influences its electron density so as to increase such propensity. In another aspect, we provide the composition obtained by combining such improved sensitizer withan image-yielding photosensitive material. In still another aspect of our invention, we provide, as new compounds, substituted dialkylaminostyryl compounds, and vinyl homologs thereof, having the formula wherein R and R are each independently selected from aromatic and aliphatic groups, n signifies from I to a plurality of --CH CH- groups, Y is selected from chlorine, bromine, nitro and methoxy and Z represents atoms selected from C, O and N necessary to complete a fused ring group containing from two to three rings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As noted, improved sensitizers of our invention are materials that upon initial exposure to light sensitize the composition to which they are added to radiation in a region of the spectrum to which the composition otherwise has lower sensitivity. Preferably, the improved sensitizer itself absorbs radiation in a region of the spectrum used for the imaging exposure and, at least in conjunction with the photosensitive composition, responds to such exposure to intensify, extend or shift the sensitivity of the system in or into a region of the spectrum to which the unexposed composition (including the sensitizer) has significantly lower sensitivity. Thus, it is preferred that the substituted sensitizer be a material which imparts selective light absorptivity to the system in which it is incorporated, which absorptivity is shiftable, extensable or, in part, intensifiable as described. In general, it is preferred that the materials have the optical properties of, or be, optical sensitizing dyes or dye bases.

For materials that can be improved by substitution in accordance with our invention, reference can be made to the above-noted Y. Yamada and T. H. Garland applications, particularly the application entitled PHOTOGRAPHIC PROCESS," and Ser. No. 523,705, now Pat. No. 3,503,745 and reference can also be made to a publication of Brooker and Vittum entitled A Century of Progress in the Synthesis of Dyes for Photography" in the Journal of Photographic Science, Volume 5, l957, pp. 71-88, the disclosure of these references being incorporated herein by reference. All of these sensitizers tend to absorb actinic energy and all have exhibited their ability to transmit the absorbed energy by a physical molecular contact or by engagement to other molecules receptive of actinic energy for purposes of modifying the photo-response. illustrative materials are compounds having a characteristic rhodamine ring structure and nominal substitution at an amino group, such as the rhodamines (i.e., aminophthaleins); materials having simple (unsubstituted) carbon chains interconnecting fused heterocyclic and benzenoid ring structures, such as pinacyanole and related carbocyanine or cyanine type dyes or dye bases; light absorbers containing heterocyclic rings fused with benzenoid rings, such as eosin dyes; and light absorbers having a triphenylmethane structure, including leuco forms thereof and compounds having thiazine, alizarine, acridine and anthraquinonoid groups or structures. In general, light absorbers having a styryl substituent such as the styryl and azastyryl dyes and dye bases styryl substituent such as the styryl dye azastyryl dyes and dye bases and vinyl homologs thereof are particularly improved when substituted in accordance with our invention and comprise a particularly preferred group of sensitizers.

As substituents, one can use any electron density influencing group and in a position on the sensitizer that allows the group to influence electron density to increase the photo- Iatensification propensity of the composition. Thus, both electron-donating and electron-withdrawing groups can be used. Examples of electron-donating groups include: F, Cl. Br, 1, OR.

II I -0CR, SR, NR NHJ3R, 0-, 5, CRa, and the like. Examples 0! electron-withdrawing groups include: N0

0 0 )5 II l CEN, CHO, R, C-0R, NR,,-|S-R, CFs,

and. the like.

In the forgoing each R is independently selected from hydrogen, aromatic groups and aliphatic groups, Note that while all of the halogens have been described as electrondonating groups they actually exhibit both electron-withdrawing and electron-donating properties with the electronwithdrawing effect becomding increasingly more important as one goes down the Periodic Group from fluorine to iodine. Accordingly, the halogens can also be included among electron-withdrawing goups.

In general, it is preferred that the sensitizer have at least one ring as part of a conjugation system, preferably as part of a fused ring group, with the electron density influencing group substituted on the ring. Generally, the position of the substituent depends on whether it is electron-donating or withdrawing. in the case of electron-donating groups it is preferred to add these to a position on the ring ortho or para to a heterocyclic atom or major functional group, or in conjugation with such ortho or para position. in the case of electron-withdrawing atoms or groups, it is preferred to add these to the meta, or conjugatively equivalent, position. However, there are exceptions to these general preferences. As noted, the halogens exhibit both electron-withdrawing and electrondonating properties. Also, some substituents increase the latensification ability of a sensitizer regardless of its position on the ring (this latter effect is particularly notable with electron-withdrawing groups).

Methods of preparing the foregoing sensitizers are well known to the art. Many sensitizers substituted in accordance with our invention are well known as are methods for their preparation. Generally, substitution of the desired electron-influencing group on a precursor to the sensitizer is a convenient method of obtaining the substituted sensitizer. As noted, substituted styryl and azastyryl dyes or dye bases and vinyl homologs thereof are particularly preferred sensitizers in our invention. It is further preferred that the sensitizer have the formula R 2/N \CH=CH/ l wherein R and R are each independently selected from aromatic and aliphatic groups, n signifies from 1 to a plurality of CH CH- groups, X is an electron density influencing group and 2 represents atoms selected from C, O and N necessary to complete the fused ring group containing from two to three rings. Sensitizers in which X is halogen, nitro, methoxy, trifluoromethyl, formyl or alkylsulfone are particularly preferred as generally more effective.

The foregoing compounds can be readily prepared by the condensation of an appropriate aromatic aldehyde, e.g., benzaldehyde, cinnamaldehyde, cinnamylidene-acetadehyde. or aldehyde having a larger number of groups, with an appropriately substituted fused ring compound. Examples of suitable fused ring dye precursors include: 4-chloroquinaldine; 2-chloropidine, 5-nitroquinaldine; 3-methyl-5- nitroisoquinaldine; 2-methyl-4-fluoro-l,8-naphthyridine; 2- methyl-5-cyano-l ,S-naphthyridine; 2-methyl-4-methoxy-l ,7-

phenanthroline; 2-me'thyl-5-formyl-l,7-phenanthroline; 3- methyl-benzo[h]isoquinoline-S-methylsulfone; 2-methyl-4- thiomethyl-SH-pyrido [2,3-d][ l,2 loxazine; 2-amino-4- methyl-5H-pyrido[2,3-d][1,2]oxazine;2-methyl-l,5-pyridine- 3-[N,N-dimethyll-carboxamide; N-4-(2-methyl-l ,5pyridinylacetamide; 2-methyl-3acetylpyrido[3,4-b]pyridine; 2-ethyl-4- methylpyrido[3,4-b]pyridine; 2-methyl-3trifluoromethylpyrido[3,2-b]pyridine; 3-bromo-4-methyl-pyridol3,2- blpyridine; 2-methyl-3-iodopyrido[4,3-blpyridine; and 3-carbomethoxy-4-methylpyrido[4,3-b]pyridine. Examples of aldehyde precursors include: p-dimethylaminobenzaldehyde; odimethylaminocinnamaldehyde; m-dimethylaminocinnamylidineaceataldehyde; o-diethylaminobenzaldehyde; m-di-toctylaminocinnamaldehyde; p-di-n-propylaminocinnamylidineacetaldehyde; m-di-sec-butyl-aminobenzaldehyde; p-

dimethylaminocinnamaldehyde; and o-dimethylaminocinnamylidineacetaldehyde.

A particularly useful group of sensitizers comprise compounds having the formula wherein R, R- n and Z are the same as above and Y is dimethylaminophenyl)-l,3,5-hexatrienyl]-4-chloroquinoline;

2-( p-dimethylaminostyryl)-4-methoxyquinoline; 4-( pdimethylaminostyryl )-2-methoxyquinoline; 2-( pdimethylaminostyryl )-4-trifluoromethylquinoline; 4-( pdimethylaminostyryl)-2-trifluoromethylquinoline; 4( odiethylaminostyryl )-2-bromoquinoline; and 2 4-( pdimethylaminophenyl)- l ,3-butadienyll-4-chloroquinoline. Derivatives of quinaldine (i.e., 2-methylquinoline) and lepidine (i.e., 4-methylquinoline) are particularly preferred.

With reference to groups designated by the letter R, it is preferred that when aliphatic they be alkyl, cycloalkyl or aralkyl, and that when aromatic they be aryl or alkaryl. It is further preferred that alkyl be from 1 to about 8 carbon atoms, cycloalkyl be from 5 to about l2 carbon atoms, arylbe from 6 to about 12 carbon atoms, aralkyl be from 7 to about l2 carbon atoms and alkaryl be from 7 to about 12 atoms.

With reference to the letter n" designating from I to a plurality of olefinic groups, n can range from 1 up to any number that is practical; the plurality of compounds thereby represented all possess similar optical properties. It is preferred that n be from 1 to 3 as these compounds are more readily prepared than higher homologs.

The following examples illustrate the preparation of sub- I stituted optical sensitizers.

EXAMPLE 1 EXAMPLE 2 One-tenth mole of each of S-nitroquinaldine and pdimethylaminobenzaldehyde were condensed using 5ml. of concentrated hydrochloric acid as a catalyst in a manner similar to that of example 1. The product was neutralized with potassium hydroxide, filtered and air dried to yield 2-(pdimethylaminostyryl)-5-nitroquinoline with a melting point of 170C.

EXAMPLE 3 One-tenth mole of each of 6-dimethylaminoquinaldine and p-dimethylaminobenzaldehyde were refluxed in 50ml. of

- acetic anhydride for five and one-half hours. The solution was neutralized with excess sodium hydroxide solution and the resultant product was chromatographed on basic alumina with benzene. The original benzene eluate was added to a 50/50 mixture of ligroin and acetone to precipitate 2-(pdimethylaminostyryl)-6-dimethylaminoquinoline as yellow prisms which were found to have amelting point of 204-207 -trifluoromethylquinaldine and 2trifluoromethyllepidine to yield, respectively, Z-(P-dimethylaminostyryl)-4-metlioxyquinoline, 4-(p-dimethylaminostyryl)-2-methoxyquinoline, Z-(p-dimthylaminostyryl)-4-trifluoromethylquinoline and 4- (p-dimethylaminostyryl)-2-trifluoromethylquinoline. g

ln general, any photographic system, organic or inorganic, which in its basic 'form is not uniformly panchromatic but which is capable of having its spectral sensitivity extended, or in part increased, can be improved by the use of a sensitizer of our invention. Suchphotosensitive systems are described in detail in the above-referenced Yamada and Garland applications. With certain photosystems, a photo-initiator may be desired, e.g., an organic halogen such as carbon tetrabromide, and the use of suchmaterials is also described in the abovenoted Yamada and Garland applications. In referring to photographic systems we intend to include not only imageyielding materials which contain color-forming ingredients but also those which yield a color upon subsequent external treatment, e.g., bywashing with a coloring agent or by printing with the material or otherwise using it as a master, or by other methods. In referring to the word image" the term is used to include images which, even in their developed state, arenot necessarily discernible to the eye but which are defined by a useful change in physical or chemical properties, such as photographic sensitivity, solubility, wettability, opticalturbidity, hardness, surface smoothness, and the like. The image may comprise a desensitization, which may be colorless, of otherwise photosensitive material in light-struck areas so that on still further treatment, color is formed in nonimage areas.

A suitable concentration of our sensitizer depends on the particular photosystem and sensitizer. Many of our sensitizers are capable of forming theirown color but this property is not important to the process except insofar as related to an ability to selectively absorb and/or transfer electromagnetic radiation. Thus, a sensitizing amount of the sensitizer is used rather than a color-forming amount, which amounts may be different. lngeneral, about 0.001 to about mg. of sensitizer per gram of image-yielding material is satisfactory.

Use of substituted sensitizersof our invention to latensify ,can be illustrated by the following example.

EXAMPLE 5 Test amounts of Z-(p-dimethylaminostyryl)-4-chloroquinoline were prepared as in example 1 and used in a formulation as follows:

20% Gelatin 50 ml. 37%.Formalin 2 drops 5% Chrome Alum 5 drops 1.5% Tergitol 4 10 drops N-vinylcarbazole 4.0 g. Carbon tetrabromide 3.2 g. 2-(p-dimethylaminostyryl)-4-chloroquinoline(4- chloro-ZSQ) 3 mg.

in ethyl acetate 2 ml.

Baryta paper was coated to about 3 mil wet thickness with the above formulation. Another baryta sheet was coated with a similar formulation but one in which 3mg. of 2-(pdimethylaminostyryl)-quinoline (2SQ) was substituted for the 4-chloro-2SQ. Test strips of each formulation were exposed for 0.2 and 0.3 seconds to a Kodachrome projection from 34 inches using a 300 Watt Bell & Howell Headliner Projector. One-half of each test strip was covered and the strips were then exposed for 60 seconds to latensifying tungsten light tiltered through a Corning CS2-59 red-passing filter (having a cut wavelength of from 6280 to 6370A) at about three feet using the Bell & Howell projector. The coverings were removed and the strips were flooded with a Sylvania Sun Gun 11" Model SG55) for one-half second at about 14 inches and then heated by passing through a rotating drum heater at about 70 C. for about ten seconds. Both test strips that were exposed for 0.3 seconds showed an image in the latensified portion and no image in the covered portion; the image obtained with the formulation containing 4-chloro-2SQ was of substantially better contrast. The test strip that was exposed for 0.2 seconds and contained 4-chloro-2SQ showed an image in the latensified portion and not in the covered portion. The test strip that was exposed for 0.2 seconds and contained ZSQ did not show an image in either the latensified or covered portrons.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of our invention.

We claim:

1. In a photographic process in which a photosensitive composition is image-wise exposed, an image is formed therein and color is developed in either the image-wise exposed areas or non-image-wise exposed areas of said composition said composition including a photoinitiator component which produce free radicals or ions upon exposure to light of a suitable wavelength, the improvement comprising the steps, prior to complete color development, of:

incorporating in said composition a sensitizing amount of a photographic sensitizing dye or dye base compound which enables an image to be developed in said composition following exposure to actinic radiation normally insufficient to produce said image, said dye or dye base compound being different from other components of said composition and having a conjugated system including at least one ring and as a substituent on said ring a group which influences the electron density of said dye or dye base compound, whereby said sensitized composition has (1) relatively low or no photosensitivity to light of a first spectral region, (2) high photosensitivity to light of a second spectral region, relative to its photosensitivity to said first spectral region, (3) photosensitivity to light of a third spectral region in portions of said sensitized com position which have been previously exposed to light of said second spectral region, and (4) a coincident range in said first and third spectral regions; imagewise exposing said sensitized composition with light of said second spectral region sufficient to radiatively modify said composition to constitute a latent image; and

blanket exposing said image-wise exposed composition with light of said coincident range to further radiatively modify those portions of the composition'constituting said latent image.

2. The process of claim 1 wherein the sensitizing compound is of a series selected from the rhodamine, pinacyanole, cyanine, eosin, triphenylmethane, thiazine, anthraquinonoid, acridine and styryl dye and dye base series.

3. The process of claim 1 wherein the sensitizing compound has the formula \N /CH=CH\ z A R wherein R and R are each independently selected from aromatic and aliphatic groups, n signifies from 1 to a plurality of --CH CH- groups, X is an electron density influencing group and Z represents atoms selected from C, O and N necessary to complete a fused ring group containing from 2 to 3 rings.

4. The process of claim 3 wherein X is selectedfrom halogen, nitro, methoxy, trifluoromethyl, formyl and alkylsulfone.

5. The process of claim 3 wherein the sensitizer is a dialkylamino-styrylquinoline.

6. The process of claim 5 wherein X is selected from halogen, nitro, methoxy, trifluoromethyl, formyl and alkylsulfone.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 3,615,430 Dated October 26 1971 Inv MS) Peter Bruck, et all It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 3, before "BACKGROUND OF THE INVENTION", insert the following material: CROSS-REFERENCE TO RELATED APPLICATIONS Related disclosures are contained in the following applications by Y. Yamada and 'I'.H. Garland: "PHOTO- GRAPHIC PROCESS, Serial No, 631,502, filed concurrently herewith; "DYE SENSITIZATION," Serial No. 523,705, filed Jaa-mery 28, now Ursa Patent No. 3,503,745;"PRODUCTION AND USE OF PHOIOSENSITIVE COMPOSITIONS AND FILMS, Serial NO. 481,759, filed August 23,. 1965, now U.S. Patent No. 3,476,562; and "DYE SENSITIZATION OF PHOTOSENSI'I'IVE NATERIALS, Serial No. 352,625, filed March 17, 1964, nowabandoned. line 27, "guinoline" should read quinoline Column 2, line 72, -CH CH" should read CH=CH- Column 4, line 12,

in" should read In line 15, should read In line 38, change 1| n 130 .v r N (CH Cn I Z ;Q\ i mfiLmn cm {a \Z /X line 45, change -CH CH-" to read -CH=CH- line 54, after of" insert -CH=CH- line 65, after "1,5-pyridinyl" insert 9 U 5 GOVERNMENT PRINTING OFFICE I9. O-356-33l,

UNITED STATES PATENT owner CERTIFICATE OF CORRECTEQN Patent NO. 3,615,430 'iJated October 26, 1971 Invent 3r(s) Peter Bruck et a1 2 It is certified that error appears in the ab veidentified patent and that. said Letters Patent are hereby corrected as shown below:

Column 5, line 8, change R r N (CEFCH) line 14, after "chlorine" change "bromide" to read bromine line 36, after "12'', second occurrence, add carbon Column 7, line 16, before "Model" add line 38,

I "produce" should read produces Column 8, line 35, change "-CH CH-" to read -CH=CH- Signed and sealed this 14th day of November 1972.

(SEAL) Attest:

LDVLARD M.FLETCHER,JR.

ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. The process of claim 1 wherein the sensitizing compound is of a series selected from the rhodamine, pinacyanole, cyanine, eosin, triphenylmethane, thiazine, anthraquinonoid, acridine and styryl dye and dye base series.
 3. The process of claim 1 wherein the sensitizing compound has the formula
 4. The process of claim 3 wherein X is selected from halogen, nitro, methoxy, trifluoromethyl, formyl and alkylsulfone.
 5. The process of claim 3 wherein the sensitizer is a dialkylamino-styrylquinoline.
 6. The process of claim 5 wherein X is selected from halogen, nitro, methoxy, trifluoromethyl, formyl and alkylsulfone. 